piano vs piano action

piano and piano action both are nouns.

Word	Noun	Adjective	Verb	Adverb
piano	Yes	Yes	No	Yes
piano action	Yes	No	No	No

piano (noun)	piano action (noun)
a keyboard instrument that is played by depressing keys that cause hammers to strike tuned strings and produce sounds	action consisting of a system of levers that move a felt hammer to strike the strings when a key is depressed
(music) low loudness

piano (adjective)	piano action (adjective)
(used chiefly as a direction or description in music) soft; in a quiet, subdued tone

piano (adverb)	piano action (adverb)
used as a direction in music; to be played relatively softly